Final answer:
Legal Regulations restrict retailer operating times, which can include various laws and standards aimed at controlling competition and enforcing safety and environmental standards.
Step-by-step explanation:
The entities that restrict the times during which retailers may operate are A. Legal Regulations. Such regulations can include licensing requirements, safety and environmental standards, zoning laws, and specific market regulations to control competition and the operational hours of businesses.
An example from history is when AT&T was the only company legally allowed to provide local and long distance phone service, which was a form of government limitation on competition. Today, zoning laws may dictate where and when businesses can operate, including restrictions for operating during evenings or on Sundays.